Mobile wireless devices, i.e. cellular telephones, personal digital assistants (PDA), etc., are constructed with an oscillator. More specifically, a mobile wireless device employing second-generation wireless telephone technology (2G) is constructed with a digital controlled crystal oscillator (DCXO) and a mobile wireless device employing third-generation wireless telephone technology (3G) is constructed with a temperature-compensated voltage controlled crystal oscillator (TCVCXO). The frequency of the oscillator (DCXO or TCVCXO) of the mobile wireless device is altered such that the mobile wireless device is synchronized with its corresponding network (i.e. 2G or 3G). The synchronization is achieved employing the time/frequency information from the corresponding network.
Mobile wireless devices can be used in conjunction with a global positioning device system (GPS) for communicating the location thereof, and thus, the mobile wireless device when incorporated into the mobile wireless device. The GPS system is constructed with a dedicated TCVCXO so that a reference clock signal thereto is uninfluenced by possible corrections of the oscillator frequency in the modem system of the mobile wireless device. The dedicated TCVCXO of the GPS system is employed to optimize parameters including time to first fix (TTFF), pseudo range, etc. The dedicated TCVCXO, by comparison with a crystal oscillator (XO), comprises a higher frequency accuracy in the case of possible temperature fluctuations (on account of the lower frequency dependence in the case of temperature fluctuations). The GPS system can also be constructed with a temperature-compensated crystal oscillator (TCXO).
The mobile wireless devices and GPS systems can be coupled together to reduce their combined cost and size by sharing the same housing and power supply, defining an integrated mobile device. To simplify the integrated mobile device and reduce manufacturing costs thereof, single components are employed to take the place of redundant components. One such redundant component is the oscillator that is located in both the GPS system and the mobile wireless device.
FIG. 1 shows a conventional integrated mobile device 100 comprising antenna 102, for transmitting a data signal to, and receiving a data signal from a mobile wireless device network; code division multiple access (CDMA) radio frequency (RF) processor 104; system TCVCXO 106 for generating and/or providing a reference frequency to various components in integrated mobile device 100; and automatic frequency control (AFC) signal 108 implemented with a frequency difference detector (not shown), a loop filter (not shown), and a digital-to-analog converter (not shown). Integrated mobile device 100 further comprises CDMA baseband processor 110 for processing a CDMA signal. CDMA baseband processor 110 includes digital-to-analog convertor (DAC) 112 and pulse density modulation (PDM) signal counter 114. A PDM signal generated from PDM signal generator 114 within CDMA baseband processor 110 is set to a predetermined bit output.
Integrated mobile device 100 further comprises GPS system 116 having GPS baseband processor 118 and GPS RF processor 120. GPS baseband processor 118 includes frequency compensation unit 122, carrier numerically controlled oscillator (NCO) 124, correlator 126, code generator 128, and code NCO 130. Carrier NCO 124 includes buffer registry (BR) 132, adder 134, and phase decoder (PD) 136. Buffer registry 132 can store a value to be added by adder 134 as a predetermined bit value. Correlator 126 outputs correlation data 138 to microcontroller unit 140.
A frequency of a CDMA signal input to integrated mobile device 100 is altered (e.g. due to motion of a user of integrated mobile device 100). A value of PDM signal counter 114 is then altered for synchronization acquisition according to the frequency change of the CDMA signal input, and thus, the output frequency of system TCVCXO 106 is altered/corrected to synchronize with the corresponding network. PDM signal counter 114 outputs the changed frequency value to frequency compensation unit 122. A value of buffer registry 132 is then altered based upon the changed frequency value via frequency compensation unit 122. This value is added to system TCVCXO 106 signal such that GPS system 116 is maintained in a locked state regardless of the automatic frequency control (AFC) operation of CDMA baseband processor 110.
It is desired to provide an improved system and method of employing a single oscillator for use by an integrated mobile device comprising both a modem system and a GPS system. The GPS system has compensation circuitry that allows the GPS system to continue to process signals when the oscillator is adjusted to maintain the mobile transmission frequency of the modem system.